1. Field of the Invention
The present invention relates to a high-frequency switching circuit, a high-frequency module including the high-frequency switching circuit, and a wireless communications device mounted with the high-frequency module, which are used particular in a multiband-compliant mobile radio terminal preferably.
2. Description of Related Art
In recent years, there have been proposed mobile phones employing a multiband system, mounted with two or more communication systems in a single mobile phone. Multiband mobile phones, which can perform transmission/reception by selecting a communication system suitable for regional characteristics, intended use, etc., are expected to be convenient ones. For example, there exist dual-band mobile phones that have two communication systems of GSM (Global System for Mobile Communication) and DCS (Digital Cellular System) as a plurality of communication systems having mutually different communication bands.
FIG. 16 is a block diagram of a high-frequency module RFM100 in a common GSM/DCS dual-band mobile phone.
The high-frequency module RFM100 comprises a transmission system TX and a reception system RX of the transmission/reception system DCS and a transmission system TX and a reception system RX of the transmission/reception system GSM, as well as a high-frequency switching circuit ASM100 adapted to demultiplex the two-transmission/reception system GSM/DCS having mutually different communication bands into the respective transmission/reception systems GSM and DCS and to switch between the transmission system TX and the reception system RX in each of the transmission/reception systems DCS and GMS.
The GSM transmission system TX provides a transmitted signal amplified in a power amplification circuit AMP100 to the high-frequency switching circuit ASM100 via a matching circuit MAT100 consisting of a low-pass filter. The transmitted signal provided to the high-frequency switching circuit ASM100 passes via a high-frequency switch and a demultiplexing circuit (demultiplexer), as will be described hereinafter, to be transmitted from an antenna ANT as a high-frequency signal. The operation above is applied similarly to the DCS transmission system TX.
On the other hand, the GSM reception system RX extracts a high-frequency signal received by the antenna ANT via the high-frequency switching circuit ASM100, and eliminates spurious signals near the reception band via a band-pass filter BPF300. The signal passes via the band-pass filter BPF300 to be amplified in an RX side low-noise amplifier AMP300 and to be input to a signal processing system. The operation above is applied similarly to the DCS reception system RX.
Meanwhile, in accordance with future developments of the market, it is expected that high-quality transmission of voice data, image data, etc., using a mobile phone unit will be provided, and to respond to these expectations, communication systems capable of transmitting large volumes of data, such as a CDMA (Code Division Multiple Access) system and next-generation communication system UMTS (Universal Mobile Telecommunications System) characterized by high data transmission rates and communication channels multiplexing, have been advancing.
To support a plurality of communication systems as mentioned above, it becomes necessary for a single module to support many more bands. This increases the demands on a multiband system such as GSM850/GSM900/DCS/PCS (Personal Communication Services)/UMTS.
Thus with the advance of band/mode multiplication, if it becomes necessary for a single high-frequency module to support many more bands/modes, certain surface layer area of a substrate with the high-frequency module mounted thereon in proportion to the number of bands/modes is to be required, which requires the high-frequency switching circuit ASM100 to be increasingly downsized.
Meanwhile, with the aim of reducing size and loss, the arrangement utilizing a high-frequency semiconductor switch such as a GaAs-SW (gallium arsenide switch) as a high-frequency switch for switching between transmission and reception in the high-frequency switching circuit ASM100 has recently been examined.
To be compliant with a multiband/multimode system such as GSM850/GSM900/DCS/PCS/UMTS using such a high-frequency semiconductor switch, it is commonly necessary, as shown in FIG. 17, to provide a high-frequency switching circuit ASM comprising: a demultiplexing circuit DIPX1 for demultiplexing a transmission/reception system into ones, respectively, for lower and higher pass bands; a high-frequency switch SW1 connected to the demultiplexing circuit DIPX1 and adapted to switch among a transmission system TX and reception systems RX in the transmission/reception system GSM850/GSM900 for example; and another high-frequency switch SW2 connected to the demultiplexing circuit DIPX1 and adapted to switch among a transmission system TX, reception systems RX, and UMTS in the transmission/reception system DCS/PCS/UMTS, for example. It is noted, in this case, that it is necessary to use a high-frequency switch that has good linearity and satisfies power resistance as the high-frequency switch SW2 to support the two different modes, i.e., GSM system and CDMA or UMTS system.
Also when using no demultiplexing circuit, it is necessary, as shown in FIG. 18, to provide a high-frequency switching circuit ASM comprising a high-frequency switch SW3 connected to an antenna terminal and adapted to switch among transmission systems TX and reception systems RX in the transmission/reception system GSM850/GSM900/DCS/PCS/UMTS.
In the arrangement utilizing the demultiplexing circuit DIPX1 as shown in FIG. 17, it is possible to support many bands by connecting the high-frequency switches SW1 and SW2 increasingly in parallel, whereby it is also possible to avoid increasing the number of terminals (number of transmitting/receiving terminals other than a common terminal) of each of the high-frequency switches SW1 and SW2.
This eliminates the need for designing and manufacturing many kinds of different high-frequency switches, in which is given a great advantage that the designing and manufacturing lead-time for such high-frequency switches or high-frequency modules including the high-frequency switches can be shortened, and further the manufacturing cost thereof can be reduced.
However, an additional part, i.e., the demultiplexing circuit DIPX1 is required, for which it is necessary to provide installation space. Therefore, there occurs a problem in that the above-described request for downsizing cannot be met.
Inserting the demultiplexing circuit DIPX1 also suffers from another problem in that there occurs a passing loss of power between the common antenna terminal and the common terminal of each high-frequency switch in both transmission and reception systems.
On the other hand, in the arrangement including no demultiplexing circuit and increasing the number of terminals in a high-frequency switch as shown in FIG. 18, it is necessary to provide a high-frequency switch according to the number of bands, which is different depending on the specification required. This requires many kinds of high-frequency switches to be designed and manufactured, resulting in many disadvantages.